Name: ______Block: ______
Science 9 – Ch. 3 Sexual Reproduction
Section 3.4 Development of the Zygote.
Once sperm and egg have fused to form a zygote, the zygote divides and becomes an embryo. The embryo is the developing organism. The embryos of sexually reproducing organisms are protected when they develop inside seeds, eggs, or the mother.
A. Seeds
· In plants, the _ovary ______becomes the ____fruit _____
o Seed- Contains __embryo ______and __stored food ______(starch or sugar)
o This food nourishes the developing plant until it is able to produce its own food using photosynthesis.
o Produced to attract animals to aid in seed dispersal
ANATOMY OF SEEDS:
Fruit formation 1 - Tomato and blackberry
When a flower has been fertilised, the petals and stamens shrivel and fall off. The ovary or ovaries begin to grow and form a fruit. Inside the fruit are the fertilized ovules, which form the seeds. When the fruit is ripe, the seeds are dispersed by a variety of methods.
The following drawings illustrate the process of fruit formation in a selection of species.
Flowering plants produce two different types of seeds. Seeds contain seed leaves,
called cotyledons
Flowering plants produce 1 of two types of seeds:
1. Monocotyledons (monocots) – Corn plants- they produce seeds with only one cotyledon
2. Dicotyledons (dicots)–
· Corn and Bean Development:
o In a corn seed ___ endosperm ______supplies _ food ______
o The radicle ______(part of the embryo) develops into __ the roots. ______The epicotyl ______becomes _____ stem and the leaves ______
o In beans: ___ the hypocotyl ____pushes through the soil and protects __ the epicotyl ______
o In corn: ____ epicotyl ______grows through a tube
Eggs:
Many animals lay eggs. Eggs that are laid contain the zygote. Some nutrients, and a mechanism for protection, such as a shell, a jelly-like substance, or an eggcase.
An egg that contains a single embryo surrounded by a shell is called an amniotic egg. The embryo is
cushioned by the amnion, which is a fluid-filled sac. The yolk sac stores food for the embryo.
The allantois holds wastes produced by the embryo. The chorion, along with the allantois, controls the
movement of gases and wastes in and out of the egg. Albumen also cushions the embryo and is an additional source of food.
Mammals that lay eggs are known as monotremes (Figure 7). There are only three living species of monotremes: the duckbill platypus and two species of spiny anteater.
3. EMBROYS THAT DEVELOP INSIDE A MOTHER:
The embryos of almost all mammals develop inside the mother.
Marsupials include kangaroos, koalas, and opossums. These animals’ embryos do not develop for very long inside the mother’s uterus, so the young are born very tiny and immature. The young actually climb from the birth canal through the mother’s fur into a pouch, where they attach to a nipple of a mammary gland. Even after they are mature enough to leave the pouch, they return to it for feeding and security.
The embryos of placental mammals, such as humans, develop inside the mother for much longer than the embryos of marsupial mammals. The word placental comes from the word placenta, which is the organ that develops around the fetus (developing offspring) and connects to the mother. The fetus is
attached to the placenta via the umbilical cord, which carries wastes out of the fetus and nutrients into the fetus.